The present invention relates to reflector for vehicular headlamps, the reference surface for which is a paraboloid of revolution and the reflecting surface of which is made up of a plural number of reflecting areas, each composed of an aggregation of reflecting segments of one of three basic configurations, a hyperbolic paraboloid, an elliptic paraboloid, or a two-sheet hyperbolic paraboloid or paraboloid of revolution, wherein the focal distance of the paraboloid-of-revolution reference surface is locally varied, not fixed, and wherein the light reflected at the boundaries between adjacent reflecting segments contributes in a positive manner to the formation of the output light distribution.
In a headlamp for a motor vehicle, in a basic construction for forming a passing beam, a coiled filament is disposed near the focal point of a reflector having the shape of a paraboloid of revolution with the center axis of the filament lying along the optical axis of the reflector, (called the filament layout of the C8 type), and a shade forming a cut line in the output light distribution pattern is disposed below the filament.
To form a desired light pattern image by the reflector, the light distribution is controlled by a lens step area on an outer lens that is disposed in front of the reflector. The resultant light distribution pattern is thus made to conform to the applicable standards.
Desired aerodynamic characteristics of the vehicle, body design, and the like frequently require the vehicle body to be shaped in a streamlined fashion. Thus, the front of the car body is often made narrow, and the headlamps must be designed in conformity with a so-called slant nose shape. In a conventional headlamp, to form a light distribution pattern having a cut line suitable for the formation of a passing beam, the lens step area of the outer lens must play a key role in light distribution control. This has the effect of limiting an increase of the angle of inclination of the outer lens with respect to the vertical axis of the vehicle. Accordingly, the conventional headlamp cannot easily be adapted for a slant nose design.
A reflector has been proposed in which a paraboloid-of-revolution surface is used as a reference surface, and a number of reflecting segments are laid out on the paraboloid-of-revolution surface. The basic configuration of each segment is a hyperbolic paraboloid, an elliptic paraboloid, or a two-sheet hyperbolic paraboloid.
The reflecting surface is divided into several reflecting area having light distribution control functions. The configurations of the reflecting segments are determined for each reflecting area in consideration of desired diffusion and converging characteristics. The projection patterns formed by the reflecting surfaces are composed into a pattern resembling a prescribed pattern. The proposed reflector thus constructed succeeds in lessening the dependency of the light distribution control on the lens step part of the outer lens.
To form the above-mentioned reflector, a reference surface is defined, which is a paraboloid-of-revolution surface of a fixed focal distance. The reflecting segments are laid out on the paraboloid-of-revolution surface in a state such that the segments contact one another at certain points on that surface. However, stepped parts are formed at the boundaries of the segments, which results in glare and hinders light distribution control.
FIG. 11(a) is a vertical sectional view schematically showing a reflecting surface a. When the focal distances for two segments b adjacent to each other in the vertical direction are equal and the focal positions thereof are the same, a horizontally extending stepped part c is unavoidably obliquely formed. Accordingly, reflected light d is directed upward, causing remarkable glare. In the figure, the x-axis is the optical axis, and the z-axis is the vertical axis.
FIG. 11(b) is a horizontal sectional view schematically showing the reflecting surface a. When the reference surfaces of segments e adjacent to each other in the horizontal direction have equal focal distances and focal positions, a vertically extending stepped portion f is formed directed toward the optical axis. The reflected light g at the stepped part f is light g directed toward the inner side of the reflecting surface. The light g cannot be controlled. In the figure, the y-axis is a horizontal axis.
If a paraboloid-of-revolution surface having a fixed focal distance is used as the reference surface, the vertical width of the reflector is determined by the focal distance, so that the freedom in selecting the width of the reflecting surface is limited. Thus, the conventional technique fails to meet the requirement of narrowing the overall width of the lamp.